GPS acuracy and local positioning system

Community General Discussions
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Hi guys,

You can skip the italic if you don't want to know the project back ground

I'm new to the forum and haven't build any robot since I used lego mindstorms in high school (9 years ago). 

I'm currently designing a robotic lawn mower for my new house.  On the mover side im fine.  Fabricating a frame, got (3) 500 watt scooter motors (2 drive and one for mower blade).  got some motor controllers for them and brakes.  Got a few agm batts.  basically i have a battery powered mower that works with RC helicopter servos controlling the speed controllers.  I want it to be autonomous.  I know several companies that make auto mowers, but they all use random pattern which i feel is waste of my energy.  They are also really slow.  This mover can mow at 5-8 mph with mower on depending on grass height, and up to 15 with blade off.  Much faster than the ones you can buy.

Since I don't know any actual programming I was considering using the NXT.  I've used the RCX in the past and found it to be quite powerful for a non programmer.  I know there are more powerful brains out there, but I'm an idiot who only knows how to use mindstorms programming from back in the day.  So, the NXT can control 3 motors and by using 2 NXT, I can control brakes as well.  With the right voltage adapters I hope to wire the NXT right into the motor controllers instead of using a servo to control the controller, but it can be done either way.

So anyways, navigation is the obvious problem.  They make a gps unit for the NXT, but GPS isnt accurate enough for mowing.  My question is, does the accuracy have a consistent offset over the course of an hour or is it constantly changing?  Could I just program in the offset each time before I mow?  would it stay accurate for an hour?  I'd like it to mow a specific path so it mows perfectly (within 3 inches) of trees and shrubs.

If GPS is out, what about local positioning system. I've heard a lot of talk but not much action.  This would be the holy grail for automated moving.  I thought about using IR for this, but the range is to short and it not super reliable, especially in sunlight.  Plus things like trees block it.  I've heard of using bluetooth, but haven't seen any one actually do it.  Is there tech out there that could make local positioning system work?

If neither of those work, what about a wire for it to follow?  I could add 2 wing mowers to my design giving it a width of 60 inches.   I would have to run wire every 5 feet staked into ground (or buried an inch) and could easily route it perfectly around trees.  If I go this route set up is a lot more pita, but I think it's the most reliable method.  Question is, how do I make it follow a wire?  What kind of current needs to run through the wire, and what kind of sensors can pick it up?  I know robomow follows the wire for edges, but I don't know what kind of sensor they have on it. 

So, Any ideas for an idiot that needs a crash course in robotics?

Thanks,

Cody

 

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My suggestion is to learn
My suggestion is to learn programming and the Raspberry Pi. This is a much more powerful computer than the Mindstorms Nxt. Also, the RasPi is powerful enough to do some image processing so that it can see where it is supposed to mow.

Second, learn as much safety as you can regarding mowers. Make sure that the mower can’t damage kids or pets. You will have created a very dangerous machine. The robot law mowers I’ve seen use trimmer line or plastic blades under a steel carriage with bumper switches all the way around to stop the mower. I’m sure there were other safety measures like reading the current used by the blade motor to make sure it’s not stuck.

Third, up your liability insurance.

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Sorry, accidental duplicate.
Sorry, accidental duplicate.

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Thanks for the

Thanks for the suggestions…I might need to actualy learn programing.  What programing language does the raspi use?  Im asusming the raspi is the hardware?

As for safty, bupers/tip/lift sensors will be integrated into final design.  (when it atonomous)  As for its current design, if it looses contant RC signal the battery disconect opens requiering a manual reset.  Im planning on adding a spring loaded brake that is held open by a servo, so if power is lost the brake slames on.  (similar to a brake on a comertial truck)   it also has a big stop button on the top that you can easily hit if it starts chasing you.

Also, my yard is fenced and it does not have enough grip/mass to break through.  (pretty safe testing enviroment)  As for robotic mower blade types, both robo mow and lawn bot use metal blades.   They do stop blades on lift, or hit…which i will integrate in when my robot gets a brain.

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How does any innovation get

duplicate

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An accellerometer may be

An accellerometer may be needed to find if the mower is tilted. A fenced environment helps greatly image processing! Some objects may fall on the grass, so image processing may detect an anormal blob of color and avoid it.

Even if it will be autonomous i suggest to watch it when it’s operating, with blades covered from upside and protected electronic from water, dust and heat.

Gps can get accurate and precise results by standing still for 1-10min depending on signal and weather condition, and has a precision of about 5 feet. Can be used to get info if if it’s not within the fence, but not for real time navigation.

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i was planningon useing igps

i was planningon useing igps as a virtual boundry.  it will be covered on top.  basicaly i have an rc robo mow that i want to make navigate better then a robomov.  Robo mow is comertialy sold and its only safty features are a bid red stop button and a bumper.  If the bumper hit it turns off blade, back up, then turns blade back on and keeps going.  also turns off if lifted up.  i will use those same features.  What they dont have is any back up boundry control.  If the wire power goes out the robo mow could easily get loose.  A simple power outage could cause this and the robomow wouldnt even know since it battery poewered.  The periiter line is powered by house electric.  it woud drive right over the perimiter at full steem ahead.  Mine will use gps to stop it if it goes out for a stroll.  Very low bumpers make mine hard to reach under without lifting it.  lifting it will turn it off once it has a brain.

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Commercially available

Commercially available robomower in europe just have a photoresistor to sense contact with ground. Up lifted = more light and switches of. A phototransistor may act as an hardware safety switch.

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Can you make some photos of the lawn?

If it’s big, plain and without obstacles it’s different from a backyard garden. The fence type may help image recognition or not work with ultrasound ranging. If the fence it’s a continuous wood fence it may work well with ultrasounds, but if it’s made from iron bars it’s not easy to detect with ultrasounds.